1. Field of the Invention
The present invention relates to a hermetically sealed container and a manufacturing method of an image forming apparatus and, more particularly, to a bonding method of an envelope of the image forming apparatus.
2. Description of the Related Art
There has been known an image forming apparatus in which a number of electron-emitting devices for emitting electrons according to an image signal are provided for a rear plate, phosphor films which receive an irradiation of the electrons, emit light, and display an image are provided for a face plate, and an inside is maintained in a vacuum state. Such an image forming apparatus often has a construction in which a supporting frame is further provided between the face plate and the rear plate, the supporting frame is bound to both of the face plate and the rear plate, and an envelope is formed. In order to allow the envelope to function as a vacuum container, it is necessary that not only a bonding portion is strictly fixed but also the bonding portion has sufficient sealing performance.
A manufacturing method of an envelope which has a bonding portion that is hermetically bound by a sealing material having a sealing function and whose hermetical bonding is reinforced by an adhesive having an adhesive function has been disclosed in Patent Document 1. According to such a technique, the sealing material is formed on one surface of the bonding portion along a circumferential length, the sealing material is heated and softened, and a member to be bound (for example, face plate) is pressed. Thus, the sealing material is fully extended to the bonding portion and high sealing performance is obtained. After that, a periphery of the sealing material is coated with the adhesive, thereby raising bonding strength. Consequently, the bonding portion having both of the sealing performance and the bonding strength is formed.
Patent Document 1: International Publication No. WO2000/51155
In the above related art, unevenness of a height of the sealing material occurs and it is demanded to further improve the hermetic sealing of the container. Specifically speaking, since the sealing material is softened when it is pressed to the member to be bound, a position of the face plate which is fixed onto the sealing material becomes unstable and there is a possibility that a thickness of bonding portion fluctuates depending on its portion. Since the sealing material is a thin member whose thickness is less than 1 mm, a small fluctuation of the thickness exerts a large influence on the sealing performance. If the sealing performance deteriorates, a vacuum degree in the envelope cannot be assured and maintained. If the position of the face plate is unstable, a possibility that the face plate is not fixed in parallel with the rear plate also occurs. There is, consequently, a risk that the unevenness of the height of the sealing material exerts a large influence on image quality.